This invention relates generally to the field of control units and methods for controlling condensing units, and more particularly to a multi-split control unit for a condensing unit having a two-stage reciprocating compressor.
A multi-split condensing unit, such as the 38HDS Multi-Split Condensing Unit made by Carrier Corp., serves two zones, allowing many indoor fan coil combinations. A multi-split application uses separate fan coils to cool separate spaces. This unit uses a fixed speed compressor and oversized fan coils, along with a head pressure control, to be able to run either two fan coils together or just one fan coil alone. The head pressure control is unwieldy and complicated.
A two speed (two-stage) compressor would fit a multi-split application better than a variable speed compressor or a fixed speed multi-evaporator system. A control system for a two stage compressor needs to handle multiple thermostat inputs and control the various stages to deliver the proper amount of cooling in an efficient manner.
Briefly stated, a two stage compressor which provides a high capacity stage and a low capacity stage is used with multiple evaporator condensing units. A control system for controlling the compressor receives inputs from two indoor locations via thermostats. The compressor runs in the low capacity stage when cooling is called for from only one of the thermostats, but runs in the high capacity stage when cooling is called for from both of the thermostats. The control system controls the transition of the compressor from the low capacity stage to the high capacity stage, and from the high capacity stage to the low capacity stage.
According to an embodiment of the invention, a control system for controlling a two stage compressor used with multiple evaporator condensing units, wherein the two stage compressor includes a low capacity stage and a high capacity stage, includes means for receiving input from first and second thermostats; means for controlling the compressor such that the compressor runs in the low capacity stage when cooling is called for from only one of the first and second thermostats, the high capacity stage when cooling is called for from both first and second thermostats simultaneously, and is off when no call for cooling is received from either first or second thermostats; means for transitioning the compressor from the low capacity stage to the high capacity stage; and means for transitioning the compressor from the high capacity stage to the low capacity stage.
According to an embodiment of the invention, a method for controlling a two stage compressor used with multiple evaporator condensing units, wherein the two stage compressor includes a low capacity stage and a high capacity stage, includes the steps of (a) receiving input from first and second thermostats; (b) controlling the compressor such that the compressor runs in the low capacity stage when cooling is called for from only one of the first and second thermostats, the high capacity stage when cooling is called for from both first and second thermostats simultaneously, and is off when no call for cooling is received from either first or second thermostats; (c) transitioning the compressor from the low capacity stage to the high capacity stage;
and (d) transitioning the compressor from the high capacity stage to the low capacity stage.